hassium, artificially produced radioactive chemical element; symbol Hs; at. no. 108; mass number of most stable isotope 265; m.p., b.p., sp. gr., and valence unknown. Situated in Group 8 of the periodic table, it is expected to have properties similar to those of osmium.

In 1984 a German research team led by P. Armbruster and G. Münzenberg at the Institute for Heavy Ion Research at Darmstadt bombarded lead-208 atoms with iron-58 ions. In 10 days of bombardment, they successfully produced three atoms of an isotope of element 108 with mass number 265 and a half-life of only 2 msec. They suggested that the new element be named hassium, which is derived from the Latin name for the German state of Hesse, where the institute is located. In 1994 a committee of the International Union of Pure and Applied Chemistry (IUPAC), convened to resolve naming disputes for the transactinide elements, recommended that element 108 be named hahnium. The name hassium was adopted internationally, however, in 1997.

See also synthetic elements; transuranium elements.